02 NB two liter AC not working

AC blew cold for years. Went from fine to no AC with one restart. Car idle surges rhythmically when I have the AC button in the on position. No sure if the compressor is engaging with AC button on and fans are not working. I will have access to gauges and VAG-COM tomorrow. All I could do today is burp the low side schrader valve a little and it does seem to have a good charge. Any ideas on a trouble shooting plan or what the problem is?

Thread by user DanG144 should have all the info you need.

That A/C system is the same as an ALH of the same year.

Fans should both come on low speed when the A/C button is pressed, so long as the key is ON. Regardless of compressor operation.

Thanks much, will dig into it.

Damn, on a NB this a PIA. Can't even find the high side port and have to attack the thermoswitch harness from the bottom.

High side port (which I never use anyway) is located in the same exact spot it is on the G/J: up by the pressure sensor near the line to the expansion valve.

Radiator thermoswitch is located down low in the exact same spot it is on the G/J.

I meant the thermoswitch is easier to get at from the bottom on a NB. I am reading the thread and in the A4 coolant Fan Testing link it says "low refrigerant pressure will lock out both fans and the AC Clutch" Does lock out both fans mean they will not come on when the AC button is pressed if the refrigerant is low?

Have not worked on this yet, is the fact that the engine surges up and down when the AC switch is on a clue?

A clue? Yes, it means the ECU is getting the signal for the A/C request and is compensating the idle speed but the compressor never kicks on.

Cool, thanks. Really fun week, lost the clutch in my 07 Jetta at 216k. I think the DMF killed itself because of noise and then an inability to depress the clutch pedal. I see a Valeo solid flywheel kit to convert it which would be much cheaper on a high mileage car. Is the vibration difference with a solid flywheel and the 2.5 motor a big deal?

Regarding the Beetle AC. Low side has 105 psi static pressure, so should be enough to run compressor, correct? I applied 12 v to the compressor connector with the car off and the clutch did not click. Is that the correct test to see if the AC clutch works?


I also get 1 for resistance between the compressor connector terminals. Clutch shot?

You can hook up a meter and you should see something around 3 ohms, if it's an open curcuit then the coil is bad. But I would think 12v should make it work.

Thanks, I guess it's compressor replacement time.

Its not that hard to change the coil.
https://www.amazon.com/dp/B071GQ7FL...jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Since you are in Wisconsin where the AC sits idle for many months, one thing has not been mentioned is that the seals on the compressor may have dried out. I believe at Auto supply stores you can buy an AC sealant which may fix your problem. Not expensive and worth a try IMO.

Regarding the coil swap. Looks like the compressor has to come out to swap the coil and it's 18 years old. Good idea, but I might just swap out the whole thing.

I don't think dried out seals is the problem because it holds 110 PSI static low side pressure.

Thanks for the help.

Fans don't turn on with AC switch on dash pushed. Will the compressor not turning on due to a bad clutch coil prevent the fans from coming on? Low side static pressure is 110, so I think there is enough refrigerant in the compressor. There is also power to the compressor connector, a test light pulses as the ECU supplies and then cuts power when the compressor does not turn on.

Sorry I didn't get back to this thread, had some stuff going on.

The FCM supplies a pulse of a bit higher voltage to pull the clutch coil in, then backs off to around 8v or so to hold it on. It takes more "oomph" to move the plate initially, but less to keep it there.

So that is why you see a pulsing on a test light. Test lights are not a good way to test this type of circuit because of this.

KOEO, if you press the A/C button (with the blower turned on...any speed) the cooling fans should both come on low speed.

Even if your fans were both dead, the compressor would still come on with the engine running and the A/C button pressed. It just won't STAY engaged, because as soon as the refrigerant pressure sensor goes too high, the FCM will turn off the compressor.

While the G/J sometimes have control heads that go bad, the NBs are FAR worse about it for some reason, even though they are wired pretty much the same way. The NBs are also FAR worse for the ignition switch connector shell getting hot and cooking, causing all sorts of electrical problems.

You can watch the A/C request in the Engine data, I forget which Measuring Group, but it is in there. That is an easy way to make sure the button's signal is getting to the ECU. Ultimately the ECU has say on compressor engagement. It will not allow the clutch to engage if: the engine is not running (no tach signal), the coolant is too high (overheating, CTS signal), full power is requested (RPM/pedal position, etc.). But this is done via a signal to the FCM, as the FCM is actually what controls the clutch power. It just does so with the ECU's permission.

Thanks for the help. Did some testing last night. Fans ran on low when jumping thermoswitch connector, but they did not run on high. There was 12V at terminal 2 of the connector. Checking for low speed power from thermoswitch there was power. Check for slow speed power from FCM, there was no power. Both fans run when powered directly at their harnesses. Looks like I might have two problems, a bad compressor coil and a bad FCM. Will switch out thermoswitch while I'm in there if that is what I do. Will check AC request from ECU as you suggested. Thanks again!